Many designs exist for the delivery of fuel to a furnace firebox.
Virtually all designs are intended to enhance combustion efficiency. In addition, tube metal temperatures and other furnace component limitations are considerations in the design of furnace fuel delivery equipment. Recently, carbon monoxide (CO) and NO.sub.x emission associated with furnace fuel combustion have entered into the factors that must be considered when designing furnace fuel delivery systems.
Poker tubes are one means of delivering gaseous fuel to a furnace firebox. Typically, the poker tubes extend from a gas plenum or manifold and protrude into the entry of the furnace firebox. One assembly is an array of poker tubes arranged around the outer periphery of the furnace burner.
Several years ago, Todd Combustion, Shelton, Conn., developed a furnace fuel delivery system that included six poker tubes arranged symmetrically around an air swirler in a furnace burner. As a result of the symmetrical arrangement of the poker tubes, the axial centers of the poker tubes form a circle around the centerline of the furnace burner. Three of the poker tubes are alternately arranged and oriented to deliver gas under pressure directly into the furnace firebox normal to the circle formed by the axial centerlines of the poker tubes. The three remaining poker tubes are arranged alternately between the poker tubes discharging gas normal to the circle formed by the axial centerline of the poker tubes and are oriented to discharge the fuel gas tangentially to the circle formed by the axial centerlines of the poker tubes. The arrangement of the prior art Todd Combustion poker tube assembly is shown in FIG. 3 herein.
The Todd Combustion prior art poker tube system functioned well, but it was believed that improvements could be made. As a result Todd Combustion expended considerable time and money on a project to improve the fuel combustion efficiency and reduce NO.sub.x emission associated with furnace fuel combustion.